$ sudo apt update
$ sudo nano /etc/apt/sources.list
$ sudo nano /etc/apt/sources.list
. . .
deb http://download.webmin.com/download/repository sarge contrib
. . .
$ wget -q -O- http://www.webmin.com/jcameron-key.asc | sudo apt-key add
$ sudo apt update
$ sudo apt install webmin
$ sudo ufw allow 10000
#open it from
https://your_domain:10000